1. Field of the Invention
The present invention relates to semiconductor memory devices, and, more particularly, to non-volatile semiconductor memory devices that can drive a charge pump and methods of controlling the charge pump.
2. Description of the Related Art
Semiconductor memory devices include volatile semiconductor memory devices and non-volatile semiconductor memory devices. The volatile semiconductor memory devices include dynamic random access memories and static random access memories. Volatile semiconductor memory devices may be featured with a fast reading and writing speed, but may lose stored content when the external power supply is removed or lost. Non-volatile semiconductor memory devices include a mask read-only memory (MROM), a programmable read-only memory (PROM), an erasable programmable read-only memory (EPROM), and an electrically erasable programmable read-only memory (EEPROM). A non-volatile semiconductor memory device keeps its content even when the external power supply is removed or lost. Thus, a non-volatile semiconductor memory device may be used to store content that must be kept regardless of whether power is supplied or not.
However, an MROM, PROM, and/or EPROM may not be easy for users to update the content of the memory because erasing and writing may not be freely done by a system. By contrast, an EEPROM is able to electrically erase and write so as to be increasingly applied to system programming or auxiliary memory devices, which require continuous update. In particular, a flash EEPROM (hereinafter, referred to as flash memory device) may be advantageous in a high capacity auxiliary memory device application because of its high integration compared to a conventional EEPROM. Of the flash memory devices, a NAND type flash memory may exhibit a high integration compared to other NOR or AND type flash memory devices.
The flash memory device programs or erases data with respect to a cell transistor using an F-N (Fowler-Nordheim) tunneling mechanism, which uses a higher voltage, for example, 20V, than the power voltage. Also, when a reading operation is performed, a voltage of about 5V-8V may be used, although it is lower than the high voltage of about 20V used in programming or erase operations.
To obtain the above high voltage for programming/erase operations or the voltage used for the reading operation, the flash memory device is equipped with a high voltage generation circuit. The high voltage generation circuit is typically embodied by using a charge pump. FIG. 1 is a timing diagram that illustrates a charge pump driving method of a conventional semiconductor memory device. Referring to FIG. 1, the flash memory device includes, for each operation section (tc1-tcn), a pumping section (thven.1-thven.n) in which a charge pump (not shown) is pumped to obtain a necessary voltage, a section in which an actual operation is performed using the voltage obtained through the pumping operation during the pumping section (thven.1-thven.n), and a recovery section (trcv.1-trcv.n) in which the charge pump is recovered.
However, the conventional charge pump driving method as shown in FIG. 1 may be inefficient when a continuous operation is performed in the continuous operation sections. For example, assuming that a section 1 (tc1) and a section 2 (tc2) are a section in which a program operation is performed, because the charge pump is pumped by the same voltage after the charge pump is recovered after the program operation in section 1 (tc1) is complete, unnecessary recovery and pumping operations are performed. Also, as shown in FIG. 1, because current is consumed during the pumping or recovery of the charge pump, the conventional charge pump driving method may cause unnecessary current consumption.